1. Field of the Invention
The present invention relates to technology for enhancing the communication quality of communication data such as voice data, when the data is relayed by transmission equipment in a network which transmits fixed-length cells, such as an ATM (asynchronous transfer mode) network.
2. Description of the Related Art
In a case where TDM (time division multiplexing) equipment are to be replaced with ATM equipment by exploiting a direction selecting function based on exchanges which are used in an existing network built up of the TDM equipment, it is requested that voice of short delay and high quality having been obtained in the TDM network be maintained even after the shift to the ATM network.
FIG. 1 is a diagram showing the architecture of a prior-art, voice data relaying system which employs TDM equipment.
In each TDM equipment 1502 for connecting exchanges 1501 as shown in FIG. 1, the delay (transmission delay) of data within the equipment is slight. Therefore, even when the voice data is relayed by the plurality of TDM equipment 1502, the delay thereof poses no problem.
However, in a case where a CODEC (coder/decoder) block being a device which codes and decodes voice data by the use of compression technology is installed in each TDM equipment 1502 in order to effectively utilize a transmission line, the relaying of the voice data by the plurality of TDM equipment 1502 results in degrading the communication quality of this voice data. The reason therefor is that the operations of voice coding/decoding are repeated for the number of times corresponding to the number of times of relaying, to increase the degradation of a voice quality attributed to the coding/decoding and the delay of the voice data attributed to voice compression.
In the example of FIG. 1, the TDM equipment 1502(#2) to which the exchange 1501(#2) of a relay station is connected between the exchange 1501(#1) in which a telephone set having called out is accommodated and the exchange 1501(#3) in which a telephone set to call to is accommodated. On this occasion, the degradation of the communication quality of the voice data increases in the two CODEC blocks which are included in the TDM equipment 1502(#2).
There have been known various techniques collectively called digital one-link relaying technology wherein, in order to prevent the delay and the quality degradation which are incurred by the coding/decoding of the voice data in the relaying office, the voice data is not coded/decoded in the TDM equipment 1502(#2) serving as the relaying office, whereby the number of times of the operations of coding/decoding the voice data matches the number of times corresponding to one link of the TDM equipment 1502.
In the example of FIG. 1, in a case where the exchange 1501(#2) does not operate as the relaying office, that is, in a case where the exchange 1501(#2) is an office to which a telephone set having called out is connected or an office to which a telephone set to call in is connected, the CODEC block of the TDM equipment 1502(#2) functions, so that the data which is transmitted between the TDM equipment 1502(#2) and the exchange 1501(#2) becomes decoded original voice data.
On the other hand, in a case where the exchange 1501(#2) operates as the relaying office, the CODEC blocks of the TDM equipment 1502(#2) do not function, so that the data which is relayed and transmitted in both ways between the TDM equipment 1502(#2) and the exchange 1501(#2) remains coded voice data.
In this case, the data which is transmitted bears passing-particular-equipment identification data for identifying whether or not the exchange 1501(#2) is to operate as the relaying office (that is, whether or not the particular equipment is to be passed). The TDM equipment 1502(#2) judges the passing-particular-equipment identification data, whereby the CODEC blocks are controlled to be valid/invalid.
Owing to such digital one-link relaying technology, voice communications of high quality can be realized in the TDM network even when a plurality of relaying equipment exist.
Meanwhile, in recent years, it has come to be eagerly requested that a TDM network be replaced with an ATM network for the purposes of heightening the transmission speed of communications and enlarging the traffic volume thereof.
FIG. 2 is a diagram showing the architecture of a prior-art, voice data switching system which employs ATM equipment 1601 substituted for the TDM equipment 1502 in the TDM network depicted in FIG. 1.
Referring to FIG. 2, a CLAD (cell assembly/disassembly) block installed in each ATM equipment 1601 is a device which assembles voice data into an ATM cell and which disassembles an ATM cell into voice data.
Besides, an ATM cell switch block installed in each ATM equipment 1601 operates as illustrated in FIG. 3. More specifically, the ATM cell switch block analyzes destination information affixed to the header part of the ATM cell which is entered from a port lying on the side of the CLAD block, so as to switch the ATM cell in the direction of a destination, and it alters the destination information of the header part to one corresponding to the next relaying destination and then delivers the resulting ATM cell to a port lying on the side of a transmission line. Also, regarding the ATM cell which is reversely entered from a port lying on the side of the transmission line, the ATM cell switch block analyzes destination information affixed to the header part of the entered ATM cell so as to switch this cell, and it alters the destination information of the header part and then delivers the resulting ATM cell to a port lying on the side of the CODEC block as corresponds to the next destination.
In general, a data transmission rate at the input/output port of an ATM cell switch block to which a CLAD block is connected is very high, so that the input/output port can process data of large traffic volume (ATM cell). In contrast, since data to be processed by the CLAD block is only voice data, a data processing rate in the CLAD block is much lower than the data transmission rate at the input/output port of the ATM cell switch block. In order to effectively use the data transmission capacity of the input/output port of the ATM cell switch block, therefore, a plurality of CLAD blocks are often connected to one input/output port.
In the architecture depicted in FIG. 2, the ATM equipment 1601 form paths which are always fixed, among the respective exchanges 1501.
With the prior art illustrated in FIG. 2, however, the process for assembling or disassembling the ATM cell for the voice data is required in the CLAD block within each ATM equipment 1601 even in the case of adopting the vocal digital one-link relaying technology which employs the passing-particular-equipment identification data or the like and which has been realized in the TDM network. The prior art therefore has the problem that delays ascribable to the cell assembly/disassembly in the two CLAD blocks within the ATM equipment 1601 to which the exchange 1501(#2) of the relaying office is connected are accumulated, resulting in the increase of a delay in the understanding of the voice data.
FIG. 4 is a diagram showing the architecture of another prior-art, voice data relaying system which employs ATM equipment 1601 substituted for the TDM equipment 1502 in the TDM network depicted in FIG. 1.
The architecture in FIG. 4 differs from the architecture in FIG. 2 in the point that a signalling termination block for receiving and analyzing the signalling information of voice is installed in each ATM equipment 1601, and that a dynamic path extending from a calling office (the exchange 1501 in which a telephone set having called out is accommodated) to a final called office (the exchange 1501 in which a telephone set to call in is accommodated) is formed in the ATM network by the controls of the signalling termination blocks.
With the architecture illustrated in FIG. 4, the ATM equipment 1601(#5) does not operate, in itself, as a relaying office for transferring voice data to-be-relayed to the exchange 1501(#4), but it directly switches the ATM cell of the voice data to-be-relayed toward the final called office by means of the ATM cell switch block.
In the above prior art shown in FIG. 4, the ATM cell for the voice data to-be-relayed is not assembled/disassembled by the CLAD in the ATM equipment 1601(#5) which operates as a relaying office for relaying the voice data, and hence, a delay ascribable to the cell assembly/disassembly does not occur in this relaying office.
The prior art shown in FIG. 4, however, has the problem that the signalling termination block needs to be installed in each ATM equipment 1601, and that management data for deciding the final called office on the basis of the signalling information is required.
Besides, with the prior art shown in FIG. 4, the main constituents of the relaying become the ATM equipment 1601, not the exchanges 1501, in the case where the conventional TDM network has been altered to the ATM network. This leads to the problem that the network topology among the exchanges 1501 existing on the network must be changed to one which is conscious of the ATM equipment 1601.
The present invention has been made with the background stated above, and it has for its object to incarnate a cell transmission network in which the network topology among exchanges as formed in a conventional TDM network can be exploited as it is, and in which the numbers of times of coding/decoding and cell assembling/disassembling operations for voice data match the numbers of times corresponding to one link of transmission equipment.
The first aspect of the present invention is premised on a cell transmission equipment (an ATM equipment 102) having a function of assembling communication data received from an exchange (101), into a cell (an ATM cell) of fixed length, and then transmitting the cell to a cell transmission network (an ATM network), a function of receiving communication data in the form of a cell, from the cell transmission network, and thereafter disassembling the cell and transmitting the resulting communication data to the exchange, and a function of determining a communication channel inside the equipment for use in connecting the equipment with the exchange, on the basis of data contained in a cell being processed within the equipment.
First, a passing-particular-equipment identification data insertion circuit (a frame generation unit 1014) inserts passing-particular-equipment identification data into the communication data to be transmitted to the exchange, the passing-particular-equipment identification data serving to identify whether or not the communication data is in a relaying state in which it is to be relayed by the particular equipment.
A passing-particular-equipment identification data reception circuit (a frame synchronization detection unit 1017) receives the passing-particular-equipment identification data from within the communication data received from the exchange.
A particular-communication-channel identification data insertion circuit (an MUX unit 1004) inserts particular-communication-channel identification data into the communication data to be transmitted to the exchange, the particular-communication-channel identification data indicating a communication channel of a cell correspondent to the communication data, when the received passing-particular-equipment identification data indicates the relaying state.
A particular-communication-channel identification data reception circuit (a particular-voice-channel identification data detection unit 1006) receives the particular-communication-channel identification data from within the communication data received from the exchange.
A cell route alteration circuit (a CLAD block 104 or an ATM cell switch block 105) alters the route of the cell inside the equipment, on the basis of the received particular-communication-channel identification data.
Owing to the above construction in the first aspect of the present invention, data processing units (for example, the CLAD blocks 104) opposing to each other can exchange the items of information on the communication channels of the cells which they are respectively processing, therebetween via the exchange. Therefore, the route of the cell inside the equipment is altered on the basis of the information, whereby the cell left intact can be relayed toward its destination without causing the communication data itself to pass through the exchange. As a result, the numbers of times of coding/decoding and cell assembling/disassembling operations for the voice data match the numbers of times corresponding to one link of transmission equipment.
In this case, the cell transmission equipment alters the relaying path of the cell on the basis of only the control of the particular equipment itself, and the exchange operates so as to receive the corresponding communication data from the data processing unit of the cell transmission equipment and to directly relay the received data to the opposing data processing unit included in the particular equipment, that is, the exchange executes the ordinary relaying operation. Therefore, the first aspect of the present invention has the feature that the network topology among the exchanges existing on the network need not be changed.
The second aspect of the present invention is premised on a cell transmission equipment (an ATM equipment 102) having a cell assembly/disassembly device (CLAD block 104) which assembles communication data received from an exchange (101), into a cell (an ATM cell) of fixed length, and then transmits the cell to a cell transmission network (an ATM network), and which receives communication data in the form of a cell, from the cell transmission network, and thereafter disassembles the cell and transmits the resulting communication data to the exchange, and a function of determining a communication channel inside the equipment for use in connecting the equipment with the exchange, on the basis of data contained in a cell being processed within the equipment.
In the first place, the second aspect of the present invention comprises a passing-particular-equipment identification data insertion circuit, a passing-particular-equipment identification data reception circuit, and a particular-communication-channel identification data reception circuit which are similar to those in the first aspect of the present invention.
Next, a particular-communication-channel identification data insertion circuit (an MUX unit 1004) inserts particular-communication-channel identification data into the communication data to be transmitted to the exchange, the particular-communication-channel identification data indicating the transmitting communication channel of the cell assembly/disassembly device (the transmission address value of the particular CLAD) which is processing a cell correspondent to the communication data, when the received passing-particular-equipment identification data indicates the relaying state.
A loop-back circuit (an SEL unit 1008) loops the cell received from the cell transmission network by the cell assembly/disassembly device, back to the side of the cell transmission network, when the passing-particular-equipment identification data which is contained in the cell assembly/disassembly device being processing the cell correspondent to the communication data received from the exchange and which has been received together with the communication data indicates the relaying state.
A cell route alteration circuit (an address/SEL control unit 1010, an address setting unit 1009) alters the route of the cell inside the equipment in the cell assembly/disassembly device, in such a way that the transmitting communication channel of the cell to be looped back is altered to one which is indicated by the particular-communication-channel identification data received from the exchange together with the communication data.
The third aspect of the present invention is premised on the same cell transmission equipment as in the second aspect of the present invention.
In the first place, the third aspect of the present invention comprises a passing-particular-equipment identification data insertion circuit, a passing-particular-equipment identification data reception circuit, a particular-communication-channel identification data reception circuit, and a loop-back circuit which are similar to those in the second aspect of the present invention.
Next, a particular-communication-channel identification data insertion circuit (an MUX unit 1004) inserts particular-communication-channel identification data into the communication data to be transmitted to the exchange, the particular-communication-channel identification data indicating a receiving communication channel of the cell assembly/disassembly device (the reception address value of the particular CLAD) which is processing the cell correspondent to the communication data, when the received passing-particular-equipment identification data indicates the relaying state.
Besides, a cell route alteration circuit (a selective reception unit 1002, an address/SEL control unit 1010) alters the route of the cell inside the equipment in the cell assembly/disassembly device, in such a way that the receiving communication channel of the cell to be received from the cell transmission network is altered to one which is indicated by the particular-communication-channel identification data received from the exchange together with the communication data.
Owing to the above construction in the second or third aspect of the present invention, the cell assembly/disassembly devices opposing to each other can exchange the items of information on the transmission and reception channels of the cells which they are respectively processing, therebetween via the exchange. Therefore, the cell received from the cell transmission network can be looped back to the cell transmission network and be relayed on the basis of the information, without executing the cell assembling/disassembling processing in each cell assembly/disassembly device. As a result, the numbers of times of coding/decoding and cell assembling/disassembling operations for the voice data match the numbers of times corresponding to one link of transmission equipment.
Also, likewise to the first aspect of the present invention, the second or third aspect thereof has the feature that the network topology among the exchanges existing on the network need not be changed.
The fourth aspect of the present invention is premised on a cell transmission equipment (an ATM equipment 102) having a function of assembling communication data received from an exchange (101), into a cell (an ATM cell) of fixed length, switching the cell, and thereafter transmitting the cell to a cell transmission network (an ATM network), a function of receiving communication data in the form of a cell, from the cell transmission network, switching the cell, and thereafter disassembling the cell and transmitting the resulting communication data to the exchange, and a function of determining a communication channel inside the equipment for use in connecting the equipment with the exchange, on the basis of data contained in a cell being processed within the equipment.
In the first place, the fourth aspect of the present invention comprises a passing-particular-equipment identification data insertion circuit, a passing-particular-equipment identification data reception circuit, a particular-communication-channel identification data insertion circuit, and a particular-communication-channel identification data reception circuit which are similar to those in the first aspect of the present invention.
In addition, a cell-switching-route alteration circuit (a routing control unit 1205) alters the switching route of the cell inside the equipment, on the basis of the received particular-communication-channel identification data.
Owing to the above construction in the fourth aspect of the present invention, data processing units (for example, the CLAD blocks 104) opposing to each other can exchange the items of information on the transmission and reception channels of the cells which they are respectively processing, therebetween via the exchange. Therefore, the switching route of the cell is altered in a cell switching circuit (an ATM cell switch block 105) on the basis of the information, whereby the cell can be directly relayed. As a result, the numbers of times of coding/decoding and cell assembling/disassembling operations for the voice data match the numbers of times corresponding to one link of transmission equipment.
Also, likewise to the first aspect of the present invention, the fourth aspect thereof has the feature that the network topology among the exchanges existing on the network need not be changed.
The fifth aspect of the present invention is premised on a cell transmission equipment (an ATM equipment 102) having a function of assembling communication data received from an exchange (101), into a cell (an ATM cell) of fixed length, and then transmitting the cell to a cell transmission network (an ATM network), a function of receiving communication data in the form of a cell, from the cell transmission network, and thereafter disassembling the cell and transmitting the resulting communication data to the exchange, and a function of determining a communication channel inside the equipment for use in connecting the equipment with the exchange, on the basis of peculiar device identification information for identifying each of data processing units included in the equipment.
In the first place, the fifth aspect of the present invention comprises a passing-particular-equipment identification data insertion circuit, a passing-particular-equipment identification data reception circuit, and a particular-communication-channel identification data reception circuit which are similar to those in the first aspect of the present invention.
Next, a particular-communication-channel identification data insertion circuit (an MUX unit 1004) inserts particular-communication-channel identification data into the communication data to be transmitted to the exchange, the particular-communication-channel identification data being the peculiar device identification information (the peculiar number value of the particular CLAD) for identifying the data processing unit (the CLAD block 104) in which the communication data to be transmitted or a cell correspondent to the communication data is processed, when the received passing-particular-equipment identification data indicates the relaying state.
Besides, a cell route alteration circuit (the CLAD block 104, an ATM cell switch block 105) alters the route of the cell inside the equipment, on the basis of the received particular-communication-channel identification data.
Owing to the above construction in the fifth aspect of the present invention, the data processing units (for example, the CLAD blocks 104) opposing to each other can exchange the items of peculiar device identification information for identifying the respective data processing units, therebetween via the exchange. Therefore, the route of the cell inside the equipment is altered on the basis of the information, whereby the cell left intact can be relayed toward its destination without causing the communication data itself to pass through the exchange. As a result, the numbers of times of coding/decoding and cell assembling/disassembling operations for the voice data match the numbers of times corresponding to one link of transmission equipment.
Also, likewise to the first aspect of the present invention, the fifth aspect thereof has the feature that the network topology among the exchanges existing on the network need not be changed.
The sixth aspect of the present invention is premised on a cell transmission equipment (an ATM equipment 102) having a function of assembling communication data received from an exchange (101), into a cell (an ATM cell) of fixed length, switching the cell, and thereafter transmitting the cell to a cell transmission network (an ATM network), a function of receiving communication data in the form of a cell, from the cell transmission network, switching the cell, and thereafter disassembling the cell and transmitting the resulting communication data to the exchange, and a function of determining a communication channel inside the equipment for use in connecting the equipment with the exchange, on the basis of data contained in a cell being processed within the equipment.
In the first place, the sixth aspect of the present invention comprises a passing-particular-equipment identification data insertion circuit, a passing-particular-equipment identification data reception circuit, a particular-communication-channel identification data insertion circuit, and a particular-communication-channel identification data reception circuit which are similar to those in the fifth aspect of the present invention.
In addition, a cell-switching-route alteration circuit (a routing control unit 1205) alters the switching route of the cell inside the equipment, on the basis of the received particular-communication-channel identification data.
Owing to the above construction in the sixth aspect of the present invention, the data processing units (for example, CLAD blocks 104) opposing to each other can exchange the items of peculiar device identification information for identifying the respective data processing units, therebetween via the exchange. Therefore, the switching route of the cell is altered in a cell switching circuit (an ATM cell switch block 105) on the basis of the information, whereby the cell can be directly relayed. As a result, the numbers of times of coding/decoding and cell assembling/disassembling operations for the voice data match the numbers of times corresponding to one link of transmission equipment.
Also, likewise to the first aspect of the present invention, the sixth aspect thereof has the feature that the network topology among the exchanges existing on the network need not be changed.